CN105162538A - Cognitive user selection method based on optimal performance - Google Patents

Abstract

A cognitive user selection method based on optimal performance. In this method, if the cognitive user can help the licensed user achieve the target rate, it can obtain the opportunity to access the spectrum of the licensed user, and the cognitive system selection can obtain the optimal performance. Cognitive users access the spectrum of licensed users. After the cognitive user accesses the licensed user's spectrum, it uses a part of the bandwidth to forward the licensed user's information to help it reach the target rate, and then uses the remaining bandwidth to send its own information. The invention effectively eliminates the problem of mutual interference between the authorized user and the cognitive user, and improves the performance of the cognitive user.

Description

A cognitive user selection method based on performance optimization

technical field

The invention belongs to the technical field of cognitive radio communication in the field of wireless communication, in particular to a cognitive user selection method.

Background technique

With the development of wireless communication technology, the number of wireless communication users continues to increase, and business demands grow rapidly. Limited wireless spectrum resources have gradually become a bottleneck restricting the development of wireless communication systems. A large number of research reports show that the utilization rate of the current wireless spectrum is only 15% to 85%. Most of the spectrum is not fully utilized most of the time, and the spectrum usage is very unbalanced. Frequency bands are often idle. It can be seen that the main reason for the shortage of spectrum resources is the existing fixed spectrum management mode and spectrum allocation strategy. Cognitive radio technology can sense the surrounding wireless communication environment, and on the premise of ensuring that the normal communication of licensed users is not affected, it can access the licensed spectrum opportunistically, which can effectively improve the utilization of spectrum resources.

In the cognitive radio coexistence spectrum access method, cognitive users access licensed spectrum under certain conditions and use the same frequency band as licensed users at the same time. Therefore, in this spectrum access method, there is always interference between cognitive users and licensed users, so that the originally very limited spectrum resources are not fully utilized, and the performance of licensed users and cognitive users will also be affected by interference. When there are multiple cognitive users in the cognitive system, the performance obtained after selecting different cognitive users to access the spectrum of the licensed user will be different.

Contents of the invention

In order to overcome the shortcomings of mutual interference between authorized users and cognitive users and low performance of cognitive users in the existing coexistence spectrum access technology, the present invention provides a method to effectively eliminate the problem of mutual interference between authorized users and cognitive users A performance-optimized cognitive user selection method for improving cognitive user performance.

The technical solution adopted by the present invention to solve its technical problems is:

A cognitive user selection method based on optimal performance, the radio communication system includes a main system and a cognitive system, wherein the authorized system is composed of an authorized user sending end and an authorized user receiving end, and the authorized system supports relay function, there is a licensed spectrum composed of a bandwidth of W; the cognitive system is composed of L cognitive user senders and a common cognitive user receiver, which tries to use possible transmission opportunities to access the spectrum of the licensed system. We assume that the cognitive system is capable of simulating the radio protocol and system parameters of the licensed system; the cooperative anti-jamming spectrum access method includes the following processes:

1) Cognitive users access the spectrum of authorized users in a cooperative manner. After receiving the information of authorized users, cognitive users help send the information of authorized users to the receiving end of authorized users through decoding and forwarding cooperation;

2) Each cognitive user ST _k calculates the rate R _p,k that can help the authorized user to achieve after accessing the authorized user spectrum;

3) Find out the set M composed of all cognitive users ST _k who can help authorized users reach the target rate R _t , M={k|k∈L,R _p,k ≥R _t };

4) Select a cognitive user ST _b in the set M, The authorized user allocates part of the time to the cognitive user and authorizes it to access its own spectrum. After ST _b accesses the spectrum of the authorized user, it uses a part of the bandwidth to forward the information of the authorized user to help it reach the target rate, and uses the remaining bandwidth to send its own Information; if M is an empty set, that is, |M|=0, it means that no cognitive user can help the authorized user reach the target rate, and the authorized user continues to send its own information through direct transmission;

The time and bandwidth allocation problem between authorized users and cognitive users is modeled as:

The following conditions

Among them, R _t represents the target rate of the authorized user, t _k represents the time taken by the authorized user to send his own information in the first time slot, and b _k represents the time used by the acquainted user ST _k to help the authorized user reach the target rate in the second time slot bandwidth. R _p,k and R _s,k respectively represent the rate obtained by the licensed user and the cognitive user after the cognitive user ST _k accesses the spectrum of the licensed user,

R _s,k ＝(1-t _k )(1-b _k )R _4,k (4)

in P _s,k represents the transmit power of the cognitive user ST _k , γ _4,k represents the channel gain of the link from the cognitive user sending end to the cognitive user receiving end, N ₀ represents the noise power spectral density, and Denote the rates obtained by authorized users in the first time slot and the second time slot respectively:

in P _p represents the transmit power of the authorized user, γ ₁ and γ _2,k represent the channel gain of the ST _k link from the authorized user’s transmitting end to the authorized user’s receiving end and to the cognitive user’s transmitting end, respectively, and γ _3,k represents the cognitive user’s The channel gain of the link from the sending end ST _k to the receiving end of the authorized user;

The above optimal time is obtained by mathematical optimization method and bandwidth allocation

Substituting (7) and (8) into (4), the rate of knowing the user is obtained as

where A=(R _2,k -R _t ), B=(R _5,k -R _d ), C=(R _2,k +R _3,k -R _5,k ), D=(R _{2, k} -R _d ).

Further, in the step 1), the cognitive user accesses the frequency spectrum of the authorized user through two time slot decoding and forwarding cooperation;

In the first time slot, occupying time t _k (0<t _k <1), the authorized user sender sends information to the authorized receiver and the cognitive user sender with all W bandwidth, so the authorized user sender sends information to the cognitive user The rate of the link at the sending end is:

In the second time slot, taking time (1-t _k ), the cognitive user sender uses b _k W (0<b _k <1) bandwidth to help send the decoded information of the authorized user sender to the authorized receiver, so The rate of the link from the cognitive user sender to the authorized receiver is:

So the rate obtained by authorized users with the help of cognitive users through two time slots is:

At the same time, cognitive users use the remaining (1-b)W bandwidth to send their own information, so the rate obtained by cognitive users is:

R _s,k =(1-t _k )(1-b _k )R _4,k (4).

Further, in the step 4), the cognitive user ST _k is selected by the following method: select the cognitive user that can obtain the optimal performance to access the frequency spectrum of the authorized user, that is, select the cognitive user ST _k , M={k|k∈L,R _p,k [i]≥R _t }, access spectrum of licensed users.

The technical idea of the present invention is: in the coexistence spectrum access method, cognitive users and authorized users use the same spectrum to communicate at the same time, and there is always interference between each other, so that the originally very limited spectrum resources cannot be fully utilized , the performance of authorized users and cognitive users will also be affected due to interference. When there are multiple cognitive users in the cognitive system, the performance obtained after selecting different cognitive users to access the spectrum of the licensed user will be different. In this patented method, the system selects cognitive users based on the best performance method to access the spectrum of authorized users through cooperation. Authorized users and cognitive users send information through different time and bandwidth, which can effectively solve the problem of authorized users and cognitive users. Interference issues between users, and improving performance for cognitive users.

The beneficial effects of the present invention are mainly manifested in: (1) eliminating the interference problem between the authorized user and the cognitive user in the coexistence spectrum access method; (2) improving the performance of the cognitive user.

Description of drawings

Fig. 1 is a schematic diagram of the anti-jamming spectrum access model of the method of the present invention, wherein, h ₁ is the channel coefficient from the authorized user sending end to the authorized receiving end, and h _2,k is the channel from the authorized user sending end to the cognitive user sending end ST _k Coefficient, h _3,k is the channel coefficient from the cognitive user sending end ST _k to the authorized receiving end, h _4,k is the channel coefficient from the cognitive user sending end ST _k to the cognitive receiving end. Suppose the path loss index ν=4, L=20, W=1, P _p /N ₀ =5dB, R _t =2.5bps/Hz, P _s,k /N ₀ =P _s /N ₀ ;

Fig. 2 is a cognitive user selection diagram, in which PT and PR are respectively located at points (0,0) and (1,0) on the two-dimensional XY axis. SR is located at (0.5,-0.5), cognitive users ST _k , k∈L={1,2,3,...,L} are randomly distributed on the midpoint of the connecting line between PT and PR, and 0.5 is the radius inside the circle. ST _b is the cognitive user selected by the method of the present invention;

Fig. 3 is a graph showing the change of authorized user and cognitive system speed with P _s /N ₀ ;

Fig. 4 is a diagram showing the variation of time and bandwidth allocation with P _s /N ₀ .

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

Referring to FIG. 1 to FIG. 4 , a cognitive user selection method based on optimal performance is realized based on an existing radio communication system. The radio communication system includes a primary system and a cognitive system, wherein the primary system is composed of an authorized user transmitter (PT) and an authorized receiver (PR). The main system supports the relay function and has a licensed spectrum composed of a W bandwidth. The cognitive user system consists of L cognitive user senders (ST _k , k∈L={1,2,3,...,L}) and a common cognitive user receiver (SR). The cognitive system is capable of simulating the radio protocol and system parameters in the host system.

In the method of this embodiment, the cognitive users access the frequency spectrum of the authorized users in a cooperative manner. After the cognitive user receives the authorized user's information, it helps send the authorized user's information to the authorized receiving end through decoding and forwarding cooperation. Each cognitive user ST _k calculates the rate R _p,k that can help the licensed user achieve after accessing the licensed user's spectrum. Find out the set M composed of all cognitive users ST _k who can help authorized users reach the target rate R _t , M={k|k∈L,R _p,k ≥R _t }. Select a cognitive user ST _b in the set M, The authorized user allocates part of the time to the cognitive user and authorizes it to access its own spectrum. After ST _b accesses the spectrum of the authorized user, it uses a part of the bandwidth to forward the information of the authorized user to help it reach the target rate, and uses the remaining bandwidth to send its own Information; if M is an empty set, that is, |M|=0, it means that no cognitive user can help the authorized user reach the target rate, and the authorized user continues to send its own information through direct transmission;

In this embodiment, after the cognitive user ST _k accesses the spectrum of the authorized user, the rate R _s,k obtained by the authorized user R _p,k and the cognitive user can be obtained by the following method:

Cognitive users access the spectrum of licensed users through decoding and forwarding cooperation in two time slots. In the first time slot, taking time t _k , PT sends information to PR and ST _k with all W bandwidth. So the rate of PT→ST _k link can be expressed as:

in, P _p represents the transmit power of the authorized user, γ _2,k is the channel gain of the link from PT to ST _k , and N ₀ is the noise power spectral density.

In the second time slot, occupying time (1-t _k ), ST _k uses b _k W bandwidth to help send the decoded PT information to PR, so the rate of ST _k →PR link can be expressed as:

in, P _s,k represents the transmit power of the cognitive user ST _k , γ ₁ is the channel gain of the link from PT to PR, and γ _3,k is the channel gain of the link from ST _k to PR. So the rate obtained by authorized users with the help of cognitive users through two time slots can be expressed as:

At the same time, cognitive users use the remaining (1-b _k )W bandwidth to send their own information, so the rate available to cognitive users can be expressed as:

R _s,k ＝(1-t _k )(1-b _k )R _4,k (4)

in, γ _4,k is the channel gain of ST _k to SR link.

The time and bandwidth allocation method in this embodiment is specifically:

The time and bandwidth allocation between authorized and cognitive users can be modeled as:

To meet the conditions

The above optimal time is obtained by mathematical optimization method and bandwidth allocation

Will and Substituting into equation (4), the maximum speed obtained by the cognitive system can be obtained as:

where A=(R _2,k -R _t ), B=(R _5,k -R _d ), C=(R _2,k +R _3,k -R _5,k ), D=(R _{2, k} -R _d ).

The cooperative anti-interference spectrum access method based on joint optimization of time and bandwidth in this embodiment can effectively eliminate the interference problem between authorized users and cognitive users in the coexistence spectrum access method, and improve the performance of cognitive users.

In the spectrum access method implemented in this implementation, in the cognitive user ST _k , Select a cognitive user ST _b to access the licensed spectrum. The cognitive users selected by the method of the present invention are shown in FIG. 2 .

In the spectrum access method implemented in this implementation, the cognitive user ST _b who chooses to access the licensed spectrum accesses the spectrum of the licensed user in a cooperative manner, taking up time (1-t _b ), and using the b _b W bandwidth obtained by a part of the access to help Forward the information of the authorized user, and use the remaining (1- _bb )W bandwidth to send its own information. Authorized users and cognitive users send information through different time and bandwidth respectively, without interfering with each other. In Fig. 3, it shows the change diagram of authorized user and cognitive system rate with P _s /N ₀ after the system selects the cognitive user ST _b who accesses the licensed spectrum; It is known that the time and bandwidth allocation of user ST _b varies with P _s /N ₀ .

Claims (3)

1. A cognitive user selection method based on optimal performance, the radio communication system includes a main system and a cognitive system, wherein the authorization system is composed of an authorized user sending end and an authorized user receiving end, and the authorization system supports The relay function has a licensed spectrum composed of a bandwidth of W; the cognitive system is composed of L cognitive user senders and a common cognitive user receiver, which tries to use possible transmission opportunities to access the spectrum of the licensed system. We assume that the cognitive system is capable of simulating the radio protocol and system parameters of the licensed system; the cooperative anti-jamming spectrum access method includes the following processes: 1) Cognitive users access the spectrum of authorized users in a cooperative manner. After receiving the information of authorized users, cognitive users help send the information of authorized users to the receiving end of authorized users through decoding and forwarding cooperation; 2) Each cognitive user ST _k calculates the rate R _p,k that can help the authorized user to achieve after accessing the authorized user spectrum; 3) Find out the set M composed of all cognitive users ST _k who can help authorized users reach the target rate R _t , M={k|k∈L,R _p,k ≥R _t }; 4) Select a cognitive user ST _b in the set M, The authorized user allocates part of the time to the cognitive user and authorizes it to access its own spectrum. After ST _b accesses the spectrum of the authorized user, it uses a part of the bandwidth to forward the information of the authorized user to help it reach the target rate, and uses the remaining bandwidth to send its own Information; if M is an empty set, that is, |M|=0, it means that no cognitive user can help the authorized user reach the target rate, and the authorized user continues to send its own information through direct transmission; The time and bandwidth allocation problem between authorized users and cognitive users is modeled as: The following conditions Among them, R _t represents the target rate of the authorized user, t _k represents the time taken by the authorized user to send his own information in the first time slot, and b _k represents the time used by the acquainted user ST _k to help the authorized user reach the target rate in the second time slot bandwidth. R _p,k and R _s,k represent the rates obtained by the licensed user and the cognitive user after the cognitive user ST _k accesses the spectrum of the licensed user, respectively, R _s,k =(1-t _k )(1-b _k )R _4,k (4) in P _s,k represents the transmit power of the cognitive user ST _k , γ _4,k represents the channel gain of the link from the cognitive user sending end to the cognitive user receiving end, N ₀ represents the noise power spectral density, and Denote the rates obtained by authorized users in the first time slot and the second time slot respectively: in P _p represents the transmit power of the authorized user, γ ₁ and γ _2,k represent the channel gain of the ST _k link from the authorized user’s transmitting end to the authorized user’s receiving end and to the cognitive user’s transmitting end, respectively, and γ _3,k represents the cognitive user’s The channel gain of the link from the sending end ST _k to the receiving end of the authorized user; The above optimal time is obtained by mathematical optimization method and bandwidth allocation Substituting (7) and (8) into (4), the rate of knowing the user is obtained as where A=(R _2,k -R _t ), B=(R _5,k -R _d ), C=(R _2,k +R _3,k -R _5,k ), D=(R _{2, k} -R _d ). 2. The cognitive user selection method based on optimal performance as claimed in claim 1, characterized in that: in the step 1), the cognitive user accesses the frequency spectrum of the authorized user through two time slot decoding and forwarding cooperative modes; In the first time slot, occupying time t _k , 0<t _k <1, the authorized user sender uses the entire W bandwidth to send information to the authorized receiver and the cognitive user sender, so the authorized user sender sends information to the cognitive user The speed of the end link is: In the second time slot, occupying time (1-t _k ), the cognitive user sender uses b _k W bandwidth to help send the decoded information of the authorized user sender to the authorized receiver, 0<b _k <1, so the cognitive user The rate of the link from the user sending end to the authorized receiving end is: So the rate obtained by authorized users with the help of cognitive users through two time slots is: At the same time, cognitive users use the remaining (1-b)W bandwidth to send their own information, so the rate obtained by cognitive users is: R _s,k =(1-t _k )(1-b _k )R _4,k (4). 3. The cognitive user selection method based on performance optimization as claimed in claim 1 or 2, characterized in that: in the step 4), the cognitive user ST _b selects by the following method: the selection can obtain the optimal performance Cognitive users access the spectrum of licensed users, that is, select cognitive users ST _k , M={k|k∈L,R _p,k [i]≥R _t }, access spectrum of licensed users.